#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    int p,d,m,s,sum=0,i=0;
    cin>>p>>d>>m>>s;
    while(sum<=s)
    {
        i++;
        sum+=p;
        p-=d;
        if(p<=m)
            p=m;
    }
    cout<<i-1;
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    return 0;
}